1. Field of Invention
The present invention relates to a transmissive screen and a rear projector.
2. Description of Related Art
Currently, there are increasing demands for rear projectors used as displays that are suitable for home theater monitors and wide-screen television sets. For example, FIG. 7 shows an optical system of a rear projector. As shown in FIG. 7, the rear projector 10 can include a housing 50 that includes therein an optical projecting unit 20, a light-guide mirror 30 for guiding images projected by the optical projecting unit 20, and a transmissive screen 40 onto which the projected images guided by the light-guide mirror 30 are projected.
The transmissive screen 40 used for the rear projector 10 should not cause moire fringes on the screen. A moire-free transmissive screen is disclosed in Japanese Unexamined Patent Application Publication No. 1-319025. FIGS. 8(a) and 8(b) are sectional view of a transmissive screen 900. FIG. 8(a) is a sectional side view of the transmissive screen 900 and FIG. 8(b) is a sectional top view of the transmissive screen 900. As shown in FIGS. 8(a) and 8(b), the transmissive screen 900 can include a Fresnel lens portion 910 having Fresnel-lens components 910a on its light-exiting face, and a lenticular lens 920 facing the light-exiting face of the Fresnel lens portion 910, the lenticular lens portion 920 having many lenticular lens components 920a on its light-incident face and black stripes 920c and protrusion 920b on the light-exiting face 920d. In addition, the distance between Fresnel-lens components 910a and/or the distance between black stripes 920c are random. Such design suppresses the generation of optical interference, and therefore the generation of moire fringes on the transmissive screen 900.
Unfortunately, this transmissive screen 900 has different diffusions on different site thereon. In more detail, diffusion differs between different sites on the transmissive screen 900, because the radius of curvature and the pitch of the lenticular lens components must be determined to achieve a desired diffusion for each lenticular lens component, i.e., the pitches of the lenticular lens components are not constant over the entire screen.
Another disadvantage of the transmissive screen 900 is a difference in interference between the Fresnel-lens components and the lenticular lens components at some sites of the transmissive screen 900. Furthermore, the overlay conditions are also different for each combination of these lens components; hence, it is difficult to prevent moire fringes at every site of the transmissive screen 900.
Another disadvantage of the transmissive screen 900 is its high cost due to the complicated manufacturing required for the Fresnel-lens components and lenticular lens components.